The Universal Mobile Telecommunications System (UMTS) is a radio communications network technology standard defined by the 3rd Generation Partnership Project (3GPP) organization.
In UMTS, a basic process of paging is related to two channels: a Paging Indication Channel (PICH), and a Paging Channel (PCH). The PICH is a fixed-rate physical channel (with the spread factor being 256), and the PICH is elaborated in 3GPP TS25.211 v4.2.0. FIG. 1 shows a frame structure of the PICH. The length of a PICH radio frame is 10 ms, which is composed of 300 bits. Of those bits, 288 bits (b0, b1, b287) bear the Paging Indication (PI), and the remaining 12 bits are reserved for future use and are not sent. One PI is composed of several bits. Depending on the length of one PI, each PICH frame may bear 18, 36, 72, or 144 PIs. The quantity of PIs carried in one PICH frame is denoted by Np. A Secondary Common Control Physical Channel (SCCPCH) bears the PCH. The PCH carries the specific content of the paging message, for example, User Equipment (UE) Identifier (ID), paging cause, and Circuit Switched (CN) domain ID. The PICH is correlated with the SCCPCH. A tail of the PICH radio frame is ahead of the SCCPCH correlated with PICH radio frame by 7680 chips.
FIG. 2 shows UE paging in a UMTS in the prior art.
After registering with a network, the UE is assigned to a paging group. Each paging group has a corresponding PI. When the UE in the paging group is paged, the PI corresponding to the paging group appears on the PICH periodically. After detecting the PI on the PICH, the UE starts receiving the specific paging message from the PCH through the SCCPCH. The upper layer of the protocol of the UE interprets the paging message.
The UE receives information in Discontinuous Reception (DRX) mode. Through the DRX mode, the UE is in a sleep mode when it is in an idle mode, and thus the power consumption is low. When the UE detects a PI of the UE, the UE awakens to receive the specific paging message. The UE monitors the PI periodically. If the period for monitoring the PI is longer, the chance for the UE to awaken is slim, and the UE is more energy-efficient. The UE, however, slowly responds to the network paging.
In UMTS, the UE obtains the content of the paging message in three steps:
Step 1. A System Frame Number (SFN) that includes the paging occasion is determined.
k indicates CN domain-specific DRX Cycle Length coefficient of the UE and the value range is 6≤k≤9; and a Paging Block Period (PBP) ranges from 4 to 64 in a TDD mode, and the PRB is 1 in the FDD mode. Therefore, in the idle mode, the DRX Cycle Length is calculated through Formula 2.1, and is expressed in radio frames.DRX Cycle Length=max(2k,PBP)  Formula 2.1Further, the SFN that includes the paging occasion of the UE is calculated through Formula 2.2.SFN={(IMSI div M)mod(DRX Cycle Length div PBP)}*PBP+n*DRX Cycle Length+Frame Offset   Formula 2.2
In the above Formula 2.2, M is the quantity of SCCPCHs that bear the PCHs; Frame Offset is the offset of the frame, which is 0 in the FDD mode; n is a non-negative integer, and the value of n is acceptable only if the calculated value of SFN is less than the maximum value 4095 of the SFN allowed by the system.
Step 2. A position of the PI to be decoded in the radio frame is determined.
The position of the PI in the radio frame is calculated through Formula 2.3 and Formula 2.4 according to an International Mobile Subscriber Identifier (IMSI) and a DRX Index of the UE.DRX Index=IMSI div 8192  Formula 2.3PI=DRX Index mod Np  Formula 2.4
The UMTS employs an SFN-based glide mechanism to calculate the actual position (q) of the PI in the radio frame more precisely. The calculation of the position (q) is performed through Formula 2.5. The SFN changes with time. The position (q) of the PI glides with the change of the SFN.
                    q        =                              (                          PI              +                              ⌊                                                      (                                                                  (                                                  18                          ×                                                      (                                                          SFN                              +                                                              ⌊                                                                  SFN                                  /                                  8                                                                ⌋                                                            +                                                              ⌊                                                                  SFN                                  /                                  64                                                                ⌋                                                            +                                                              ⌊                                                                  SFN                                  /                                  512                                                                ⌋                                                                                      )                                                                          )                                            ⁢                      mod                      ⁢                                                                                          ⁢                      144                                        )                                    ×                                      Np                    144                                                  ⌋                                      )                    ⁢          mod          ⁢                                          ⁢          Np                                    Formula        ⁢                                  ⁢        2.5            
Step 3. The PCH is read to obtain the specific content of the UE paging message.
Pq denotes the value of the PI in the position q. If Pq=0, it indicates that the PI is invalid, and the UE dose not need wakeup. If Pq=1, it indicates that the PI is valid, and the UE needs wakeup. According to the corresponding position relation between the PICH and the SCCPCH that bears the PCH, the specific content of the paging message is read.
As described above, in UMTS, the UE calculates the SFN that includes the paging according to the IMSI and the DRX Index, and uses Np to calculate the actual position (for example, bit position or bit group position) of the PI to be decoded in the radio frame. The UE reads the PCH according to the corresponding position relation between the PICH and the SCCPCH that bears the PCH, and obtains the specific content of the UE paging message.
Meanings of the symbols involved in the foregoing formula (applicable to the following text) are: mod means modulo operation, div means division and round-off, L means round-down, and max (a, b) means a greater value among a and b.
A Long Term Evolution (LTE) project is intended for the mobile communication architecture to be developed by the 3GPP organization in the coming 10 years. FIG. 3 shows a structure of a radio frame applied in LTE. One frame is 10 ms, and is composed of 10 radio sub-frames, with each radio sub-frame being 1 ms. One radio sub-frame includes two timeslots, namely, each timeslot is 0.5 ms.
FIG. 4 shows a structure bearer of a radio sub-frame applied in LTE. One radio sub-frame includes 14 Orthogonal Frequency Division Multiplexing (OFDM) symbols, where the first three OFDM symbols bear the Physical Downlink Control Channel (PDCCH), and the last 11 OFDM symbols bear the Physical Downlink Shared Channel (PDSCH). The PDCCH bears the Paging Radio Network Temporary Identifier (P-RNTI), and the PCH mapped onto the PDSCH bears the specific content of the paging message.
The prior art described above reveals that: Compared with UMTS, LTE does not define PICH or PI, but defines a PCH for bearing the paging content. Meanwhile, the channel bearer unit changes from the 10-ms radio frame to the 1-ms radio sub-frame. There are many other systems like the LTE whose physical channel type and structure are different from those of the UMTS. In such systems, the computation of the paging occasion in UMTS in the prior art is not applicable any more, and such systems are unable to determine the paging time.